docs: document server.preTransformRequests

[wahidrizka]

What

server.preTransformRequests is part of the public ServerOptions type and carries its own JSDoc and @default, but grep -rn "preTransformRequests" docs/ returns nothing. The only way to discover it today is reading packages/vite/src/node/server/index.ts.

It is also the odd one out next to server.warmup, which sits in the same interface, controls closely related behaviour, and is documented.

Changes

Adds a ## server.preTransformRequests section to docs/config/server-options.md, placed between server.warmup and server.watch. It covers:

• the type and default, taken from the existing JSDoc on ServerOptions.preTransformRequests
• what it does: importAnalysis calls environment.warmupRequest() for every static local import of a module it transforms, so those modules are ready before the browser asks for them
• that dynamic imports are not pre-transformed
• that server.open's early-crawl optimisation depends on it (server/index.ts guards that path with if (server.config.server.preTransformRequests))

What I checked

The one internal link I used, #server-open, already resolves: ## server.open exists in the same file and docs/config/preview-options.md links to it the same way. The code sample matches the formatting of the server.warmup sample directly above it.

I did not run pnpm run test-docs locally, since it needs a full monorepo install and build to be meaningful. The change is markdown only, with no new anchors and no new external links.